Ferdie, wearing an orange gear vest with a bell on his neck, has been a rescue dog most of his life, Terpstra said. They worked the Oso slide together.

Suzanne Elshult, of Edmonds, and her dog, Keb, train 15 hours a week in all kinds of environments, including schools and the wilderness, she said.

In training, the dogs constantly are rewarded for good behavior.

In the field, families often are watching the dogs work. The handlers have to modify the ways they praise the dog to reflect the somber task.

“We whisper encouraging words and give them some TLC,” Elshult said.

On Friday, the state Department of Agriculture sent its Reserve Veterinary Corps to provide additional medical care for dogs working in the slide zone.

The dogs have been working in 90-minute shifts. So far, they have been treated for cuts, hypothermia and paw injuries. Each dog must be decontaminated before leaving the scene.

The volunteer veterinarians expect to stay in Oso for at least another two weeks.

Some dogs are trained to find people who are alive, some are trained to find remains, and some can do both, said Everett police Sgt. Kelly Carman, who has worked as a dog handler and trainer in military and police roles since 1980.

Common breeds include German shepherds and Labrador retrievers — dogs bred over time to hunt and to work, she said.

“They not only have this phenomenal sense of smell, they’re also highly trainable, and they want to please their handler, which makes it a lot easier to train them,” Carman said.

The training is similar in concept to the training for drug-detection and bomb-detection dogs in that it’s based on particular scents, Carman said.

A good search dog relies on its hunting instincts and the millions of scent cells in its snout, said Marcia Koenig, a King County Search and Rescue volunteer who’s been working with search dogs more than 40 years.

Rescue dogs often are medium to large breeds so they can cover ground but still get into small spaces, she said.

Well-trained search dogs respond strongly to rewards of “food or play or both,” Koenig said. “The dog is working to get its reward, not because they’re altruistic. What we’re doing is we’re taking the natural behavior of the dog, which is looking for prey, and we’re just slightly shaping it to find people.”

The dogs must be able to work off-leash and follow commands, even if their owners are some distance away.

“If you say go away, your dog is going to go away,” Koenig said. “If you use your arms and gesture to the right or the left, the dog will actually go in that direction.”

Handlers are trained to observe changes in the dog’s behavior. Their breathing might change. If they know they’ve found something, they might bark, sit or lie down.

In watery or muddy conditions, the dogs’ reactions often can help narrow the search even if they can’t pinpoint a location.

“When you’re working a situation like a disaster, a mudslide, a water search or a snow search, you’re looking for somebody who is concealed,” Koenig said.

Dogs trained to find missing people can home in on a person’s particular scent. They’re more often deployed in urban environments to find missing kids or older people with memory loss.

Certified working dogs must train as often as once a week to maintain their skills.

There’s a human component though, too.

Dogs arriving at a scene signifies to a family that resources are being deployed, that the search is active and ongoing, Carman said.

“Most people love dogs and when you’ve got dogs around, it tends to lift people’s spirits,” she said. “People are aware of dogs’ capabilities and when they see dogs on scene, it helps the families because they realize the authorities are doing everything they possibly can.”

Still, it’s important to note that dogs are just one rescue tool, and it takes people to get the work done, Koenig said.